Not applicable.
Not applicable.
(1) Field of the Invention
The present invention generally relates to circuit device packages. More particularly, this invention relates to a multi-chip module (MCM) and method adapted to permit both underfilling and overmolding of surface-mounted devices on opposite surfaces of a laminate substrate within the MCM.
(2) Description of the Related Art
A flip chip is generally a surface-mounted (SM) device in the form of a monolithic semiconductor chip, such as an integrated circuit (IC) chip, having bead-like solder terminals formed on one of its surfaces. The terminals, also referred to as solder bumps, serve to both secure the chip to a circuit board and electrically interconnect the flip chip circuitry to a conductor pattern formed on the circuit board, which may be a ceramic substrate, printed circuit board (PCB), printed wiring board (PWB), flexible circuit, or a silicon substrate.
While typically mounted directly to a substrate, flip chips have been incorporated into packages, an example of which is ball grid array (BGA) packages. An example of a BGA package 110 is shown in FIG. 1 as including an IC semiconductor chip 112 that is wire bonded to a substrate 114, e.g., a laminate PCB, with wires 116. The wires 116 are electrically connected through vias (not shown) in the substrate 114 to terminals 118 on the opposite surface of the substrate 114. Similar to the flip-chip process, the terminals 118 serve as interconnects between the chip 112 and a conductor pattern on a circuit board (not shown) to which the BGA package 110 will be mounted. FIG. 2 is an example of the use of a flip chip 122 in a BGA package 120 to form a single-chip module. The flip chip 122 is equipped with solder bumps that form solder joint connections 126 when the chip 122 is flip-chip mounted to a conductor pattern on a substrate 124, e.g., a high-density PCB, which can then be mounted to a circuit (mother) board (not shown) with terminals 128 on the lower surface of the substrate 124. In the case where the substrate 124 is a PCB, it is desirable to underfill the flip chip 122 with a filled epoxy 130 to ensure the reliability of the solder joint connections 126. Finally, FIG. 2 shows the interior of the BGA package 120 comprising a molding compound 132 that overmolds the chip 122.
While the packaging technique of FIG. 2 capitalizes on the processing and assembly advantages provided by flip chips and BGA""s, further improvements in packaging processes and density are continuously sought. For example, the underfilling process is both cumbersome and expensive, and becomes more difficult as the number of flip-chips mounted to a substrate increases, especially if the chips are to be mounted to both surfaces of the substrate.
The present invention provides a package and packaging method that incorporate multiple surface-mounted devices, such as flip chips, mounted to a chip carrier, which in turn can be mounted onto a circuit board. The package is configured to provide a cost-effective, high-density multi-chip module that is also configured to facilitate underfilling and/or overmolding of circuit devices mounted on both sides of the chip carrier.
The package of this invention generally includes a pair of laminate substrates that together form a chip carrier and input/output (I/O) interface structure for a number of chips, e.g., flip chips, wire-bonded chips and/or other surface-mount components. A first of the laminate substrates has a first conductor pattern on a first surface thereof and a second conductor pattern on an oppositely-disposed second surface thereof. The second laminate substrate is attached to the first laminate substrate, and has an interior opening therethrough that is surrounded by a frame portion. The frame portion has a first surface facing the first laminate substrate and an oppositely-disposed second surface on which solder terminals are present. One or more surface-mounted devices are mounted to each of the first and second surfaces of the first laminate substrate. The first and second laminate substrates are attached to each other such that the surface-mounted device mounted to the second surface of the first laminate substrate is disposed within the interior opening of the second laminate substrate.
In view of the above, the present invention provides a process for forming an MCM package in which one or more surface-mounted devices are located within a cavity defined by the interior opening in the second laminate substrate. The second laminate substrate is preferably configured with lateral openings, preferably located in its first surface and therefore between the first and second laminate substrates. Through one of these lateral openings, a molding compound can be injected into the cavity defined by the interior opening in the second laminate substrate, with the result that the device mounted to the second surface of the first laminate substrate can be simultaneously underfilled and overmolded. As such, the present invention provides a dual-sided MCM package that can be equipped with flip chips on opposite surfaces of a laminate substrate. Advantages include a relatively lowcost, electrically testable package whose surface-mounted devices can readily be both underfilled and overmolded to promote the reliability of the package.
Other objects and advantages of this invention will be better appreciated from the following detailed description.